Airfoil Casting Methods

ABSTRACT

In the castings of a turbine element, a sheet casting core is assembled to a feedcore. The sheet casting core and feedcore are placed in a die. A sacrificial pattern material is molded over the casting core and feedcore to form a pattern including an airfoil. The sheet casting core extends from at or adjacent a trailing edge of the airfoil. The sheet casting core has a first array of open areas and a second array of portions interspersed with the open areas. A first portion of the die has a third array of projections contacting the second array.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of Ser. No. 11/600,416, filed Nov.14, 2006, and entitled “Airfoil Casting Methods”, the disclosure ofwhich is incorporated by reference herein in its entirety as if setforth at length.

BACKGROUND OF THE INVENTION

This invention relates to gas turbine engines, and more particularly tocooled turbine elements (e.g., blades and vanes).

In the exemplary cooling of turbine elements, air from the engine'scompressor bypasses the combustor and cools the elements, allowing themto be exposed to temperatures well in excess of the melting point of theelement's alloy substrate. Trailing edge cooling of the element'sairfoil is particularly significant.

In one common method of turbine element manufacture, the mainpassageways of a cooling network within the element airfoil are formedutilizing a sacrificial core (e.g., a molded ceramic core) during theelement casting process. The airfoil surface may be provided with holescommunicating with the network. Some or all of these holes may bedrilled. These holes may include film holes on pressure and suction sidesurfaces and holes along or near the trailing edge. U.S. Pat. No.4,601,638 discloses the casting of trailing edge cooling passageways bya portion of the ceramic core. U.S. Pat. No. 7,014,424 discloses thecasting of trailing edge cooling passageways by a refractory metal coreassembled to a ceramic feedcore.

SUMMARY OF THE INVENTION

Accordingly, one aspect of the invention involves a method for casting aturbine element. A sheet casting core is assembled to a feedcore. Thesheet casting core and feedcore are placed in a die. A sacrificialpattern material is molded over the casting core and feedcore to form apattern including an airfoil. The sheet casting core extends from at oradjacent a trailing edge of the airfoil. The sheet casting core has afirst array of open areas and a second array of portions interspersedwith the open areas. A first portion of the die has a third array ofprojections contacting the second array.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a turbine blade.

FIG. 2 is a streamwise sectional view of an airfoil of the blade of FIG.1, taken along line 2-2.

FIG. 3 is an enlarged view of a trailing portion of the airfoil of FIG.2.

FIG. 4 is a spanwise sectional view of the airfoil of FIG. 3.

FIG. 5 is a partial view of pressure side cooling outlets of the airfoilof FIG. 3.

FIG. 6 is a partial view of a core assembly.

FIG. 7 is a streamwise sectional view of a pattern die before waxinjection.

FIG. 8 is a partial view of a pressure side die part of the pattern die.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a turbine blade 20 having an airfoil 22 extending along alength from a proximal inboard end/root 24 at an inboard platform 26 toa distal end 28 defining a blade tip. A convoluted “fir tree” attachmentroot 29 depends from the underside of the platform 26 for mounting theblade to a complementary slot in a disk (not shown). A number of suchblades may be assembled to the disk side by side with their respectiveplatforms forming an inboard ring bounding an inboard portion of a flowpath. In an exemplary embodiment, the blade is unitarily formed of ametal alloy.

The airfoil extends from a leading edge 30 to a trailing edge 32. Theleading and trailing edges separate pressure and suction sides orsurfaces 34 and 36 (FIG. 2). For cooling the airfoil, the airfoil isprovided with a cooling passageway network 40 (FIG. 1) coupled to ports42 in the root 29. The exemplary passageway network includes a series ofcavities extending generally lengthwise along the airfoil. An aftmostcavity is identified as a trailing edge cavity 44 extending generallyparallel to the trailing edge 32. A penultimate cavity 46 is locatedahead of the trailing edge cavity 32. In the illustrated embodiment, thecavities 44 and 46 are impingement cavities. The penultimate cavity 46receives air from a supply cavity 48 through an array of apertures 50 inthe wall 52 separating the two. The exemplary supply cavity 48 receivesair from one or more of the ports 42. Likewise, the trailing edge cavity44 receives air from the penultimate cavity 46 via apertures 56 in thewall 58 between the two.

FIG. 3 shows a trailing edge portion of the airfoil including a trailingedge cooling slot 70 extending from an inlet 72 at the cavity 44 to anoutlet 74 at the trailing end of the airfoil pressure side 34. The slot70 has pressure and suction side wall surfaces 76 and 78 along pressureand suction side walls 80 and 82 of the airfoil. An exemplary slotheight H between the surfaces 76 and 78 is an essentially constant 2.5mm, more broadly 2-3 mm or 1.2-7.6 mm. An exemplary slot streamwiselength L_(S) is 12.7mm, more broadly 10-15 mm. An exemplary outletlength L_(O) (streamwise and parallel to the slot) is 2.54 mm, morebroadly 2-3 mm.

FIG. 4 shows further details of the slot 70. The exemplary slot 70includes a number of posts spanning between the surfaces 76 and 78. Theexemplary slot includes a first/upstream/leading array of posts 90, asecond array of posts 92, a third array of posts 94, a fourth array ofposts 96, a fifth array of posts 98, and a sixth/downstream/trailingarray of posts 100. Each of the exemplary arrays 90-100 extendsessentially spanwise along the airfoil. The size and cross-sectionalshape of the posts, the pitch or spacing within an array, the pitch orspacing between arrays, and the relative phases of the arrays may beselected to achieve desired airflow and heat transfer properties. Theexemplary trailing posts 100 are streamwise elongate of near teardropplanform. The posts 100 have width W_(P) and length L_(P).

Between each of the trailing posts 100 the pressure side wall 80 has asmall recess 120 (FIG. 5) forming an upstream/portion of the outlet 74.Along the recess 120, the pressure side wall 80 has a trailing portion122. The exemplary trailing portion 122 is arcuate and downstreamconcave to merge with the adjacent posts 100.

In an investment casting manufacturing process, the main passageways ofthe airfoil may be cast against a sacrificial ceramic feedcore. The slot70 may be cast against a refractory metal core (RMC) assembled to thefeedcore. The core assembly may be molded within sacrificial material(e.g., wax) of an investment casting pattern. A ceramic shell may beformed over the pattern (e.g., in a multi-stage stuccoing process). Thesacrificial material may be removed (e.g., in an autoclave), leaving thecore assembly within the ceramic shell. In such a process, the patternmay have surface features corresponding with or essentially identical tocorresponding external surface features of the turbine element to becast. These features form inverse surface features of the associatedshell and are, themselves, molded against inverse features of anassociated die.

FIG. 6 shows a refractory metal core 180 assembled to a ceramic feedcore182. FIG. 7 shows the core assembly mounted in a pattern molding die.The exemplary RMC 180 is formed as a sheet of essentially constantthickness T_(S) between first and second surfaces (faces) 184 and 186generally along pressure and suction sides. The faces 184 and 186 extendbetween a leading/upstream end 188 and a trailing/downstream end 190(FIG. 6). The faces also extend between first (e.g., inboard) and second(e.g., outboard) spanwise ends 192 and 194. A leading portion 196 (FIG.7) of the RMC is captured within a trailing slot 200 in a trailing leg202 of the feedcore.

FIG. 6 further shows the RMC as including arrays of through-holes 204,206, 208, 210, 212, and 214 complementary to and for casting the posts90, 92, 94, 96, 98, and 100, respectively. To facilitate flexing of theRMC out of a planar configuration, the exemplary RMC has a series ofrelief notches 216 each extending to a single one of several of theholes 214.

FIG. 7 shows the exemplary die as including a series of die elements220, 222, and 224. The elements combine to define a cavity 228 forreceiving wax to be molded over the core assembly. The die elements 220,222, and 224 may be assembled over the core assembly by relativetranslations in associated pull directions 510, 512, and 514. Aftermolding, separation of the die elements may be by a reverse translation.In the exemplary die, the first element 220 falls generally along thepressure side of the airfoil portion of the cavity and pattern. Thesecond element 222 falls generally along the suction side. The thirdelement 224 has a relatively small extent along a cavity 228 just at thetrailing edge thereof. In the exemplary die, a portion 230 of the RMC200 extending beyond the trailing edge is captured between the first andthird die elements 220 and 224.

According to the present invention, the pattern includes recessescorresponding to the recesses 120 in the wall 80. To provide theserecesses, in the exemplary die the first element 210 includes a spanwisearray of projections 240 (see also FIG. 8). FIG. 8 also shows a surfaceportion 242 of the die element 210 for molding the pressure side surfaceof the pattern. This surface portion 242 includes a trailing array ofportions 244 alternatingly extending between the projections 240 formolding the exposed pressure side surfaces of the trailing array ofpattern posts (corresponding to the airfoil posts 100). FIG. 8 furthershows a surface portion 250 for contacting the pressure side surface 184of the RMC downstream of the surface portion 242 and projections 240.

The present teachings may be implemented to manufacture a reengineeredturbine element as a replacement for an existing element (or elementconfiguration). An exemplary existing element may be manufactured usinga molded ceramic core to provide both the feed passageways and theoutlet passageways. The present teachings may permit finer features tobe formed in the outlet passageway (e.g., a passageway with a smallerheight, more and differently shaped posts, and the like). In such animplementation, the projections 240 may provide similar ultimatefeatures in the wax pattern to features molded by projections from thetrailing portion of the baseline ceramic core. However, in the presentimplementation, the recesses formed by these projections would be filledduring the shelling process rather than being formed over and remainingfilled by the core projections.

One or more embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, when implemented as a reengineering of an existing turbineelement or using existing equipment, details of the existing element orequipment may influence details of any particular implementation.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A method comprising: assembling a sheet castingcore to a feedcore; placing the sheet casting core and feed core in adie; and molding a sacrificial pattern material over the sheet castingcore and feedcore to form the pattern including an airfoil and the sheetcasting core extending from at or adjacent a trailing edge of theairfoil, wherein: the sheet casting core has a first array of open areasand a second array of portions interspersed with the open areas; and afirst portion of the die has a third array of projections contacting thesecond array.
 2. The method of claim 1 wherein: the placing comprisespositioning relative to a first die element and then assembling a seconddie element to the first die element.
 3. The method of claim 1 wherein:the molding comprises introducing a wax as said sacrificial patternmaterial.
 4. The method of claim 1 wherein: the assembling is entirelybefore the placing.
 5. The method of claim 1 wherein: the third arrayfalls along a pressure side of the airfoil; and the third array includes5-50 such projections.
 6. The method of claim 1 wherein: the feedcorecomprises a molded ceramic; and the sheet casting core consistsessentially of a refractory metal-based member, optionally coated. 7.The method of claim 1 wherein: the sheet casting core has a thickness of1.2-7.6 mm along a majority of a surface area.
 8. The method of claim 1wherein: the sheet casting core has an essentially uniform thickness of2-3 mm along a majority of a surface area.
 9. A casting core and dieassembly for molding an airfoil pattern having pressure and suctionsides, the assembly comprising: a feedcore; a sheet casting coreassembled to the feedcore; a die at least partially containing thefeedcore and sheet casting core and including first and second surfacesections shaped to respectively form the airfoil pattern pressure andsuction sides; and means on the die and sheet casting core for formingan array of trailing edge slots open along one side of a pressure sideand a suction side of an airfoil to be cast via the airfoil pattern. 10.The assembly of claim 9 wherein: each of the slots has an opening alongsaid one side having a length and a width; and for at least some of theslots, the length is at least 50% of the width.
 11. The assembly ofclaim 9 wherein: the one side is the pressure side of the airfoil. 12.The assembly of claim 9 wherein: each of the slots has an opening alongsaid one side; and for at least some of the slots, opening has anarcuate leading extremity.
 13. The assembly of claim 9 wherein: thefeedcore consists essentially of a ceramic; and the sheet casting corecomprises a refractory metal-based sheet.
 14. The assembly of claim 9wherein: the sheet casting core has a thickness of 1.2-7.6 mm along amajority of a surface area.
 15. The assembly of claim 9 wherein: thesheet casting core has an essentially uniform thickness of 2-3 mm alonga majority of a surface area.